Effects of Sea‐Level Rise on Dredging and Dredged Estuary Morphology

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Abstract
Estuaries and deltas worldwide are facing land loss and drowning due to sea‐level rise (SLR). Commonly home to ports, their channels are dredged and deepened for navigation. However, little is known about how such sediment management will interact with changing sediment transport patterns due to SLR. Using scale experiments, empirical relations and real world examples from global estuaries and deltas, we identify that dredging and SLR combined enhance bend migration whereas SLR alone leads to decentralizing of channels and drowning of intertidal area. In estuaries where channels are fixed, excess energy due to increasing tidal prism will manifest as bed and bank erosion, placing flood safety measures like dikes at risk. SLR increases dredging volumes in upstream reaches due to the rapid collapse of shoals and river banks along the whole estuary. Channel deepenings are ineffective under SLR conditions due to sediment import induced by increasingly flood‐dominant tides. Non‐dredged systems which have more regular and level elevations will lose intertidal area more quickly than dredged systems that have disconnected higher intertidal flats and a single deep channel. Mid‐size dredged European systems are more likely to drown due to dredging in the present century than from SLR. Effects can be avoided by pursuing sediment management strategies that help restore the morphology disrupted by dredging.

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